Add linting #179

I work for Indeed, and I recently filed a bug for a missing null check in embedded entries that was fixed (thanks!) that crashed our entire page.

That's a pretty obvious and easy issue, so I was surprised a linter didn't find that for you. I checked and you're using tslint, which has been deprecated since 2019.

I think you'd be able to anticipate and fix a lot of these bugs if you added up to date linting.